Head gaskets for internal combustion engines must be designed to withstand the high temperature which are generated in the engine and have, therefore, been formed in the past from composite materials and materials which, like asbestos, are resistant to high temperatures.
Since such gaskets are required to seal fluid passages which may be under pressure and which can be traversed by a variety of fluids, the gasket must be capable of withstanding these substances as well. The gaskets also must be capable of withstanding significant compressive forces of the type required to effect a perfect seal so that various fluids do not intermingle and so that leakage to the outside or into the cylinder is prevented. The seal must also be capable of maintaining the pressure within the cylinder so that there is no loss of compression, and in addition, must be capable of limited deformation so as to compensate for manufacturing tolerances and planetary differences of the mating surfaces of the cylinder head and the cylinder block onto which the cylinder head is mounted.
A cylinder head gasket for this purpose can comprise a generally planar body which, around at least the cylinder-bore hole, is formed as a so-called fire ring with a metal lining for the compressible material which otherwise forms the body of the gasket.
This body is provided not only with the hole adapted to seal the cylinder bore and to form the fire ring, but also with an assortment of other holes for the various purposes described.
Certain of these holes, for example, can be traversed by coolant, generally a water/glycol mixture or some other antifreeze or coolant composition.
Other holes are provided to communicate between the lubricant passages in the cylinder block and the cylinder head and are thus traversed by the engine oil. Still other holes, of course, are traversed by the bolts which secure the cylinder head to the cylinder block.
While it is possible for automotive engines generally to utilize a single head gasket for a row of cylinders and a respective cylinder head, it also has been proposed, especially, for heavy-duty engines, to provide a plurality of cylinder heads, each of which can be assigned to at least one cylinder and which is provided with a respective head gasket. In this case, the head gasket has a central opening which is aligned with the cylinder and a pair of lateral wings or regions, each of which can be provided with a plurality of the fluid ports previously mentioned and with respective holes for the corresponding bolts.
The latter construction is particularly of interest because it permits the same head gasket to be used for various types of engines, e.g. V-6, V-8, in-line 6 or in-line 8 engines, regardless of the engine construction (V or in-line) and regardless of the number of cylinders.
In practice although the number of gasket elements which may be required for an engine is increased, the overall cost is reduced because the number of different types of gaskets which may be stocked is less and the unit cost of the gasket, of course, also less, or possibly even lower than the per cylinder cost of a gasket adapted to be used for a multiple cylinder head.
With these gaskets as well, a fire ring is provided around the opening or openings to be traversed by hot gases, i.e. the cylinder opening or openings. It is also possible to surround the openings which are to constitute liquid passages with borders or ribs of elastomeric material to increase the resilience in these regions and the sealing effectiveness. The balance of the gasket, constituting the body thereof, should be composed of a material which should, if possible, be free from asbestos, because of the detrimental effects of this mineral, but having a good resistance to gas and to heat. Indeed, the body or central plate can be composed of a metal of good quality.
The elastomeric cords or ribs can be molded onto the metal body in a mold into which the body is inserted and it has been the practice, as a consequence, to accommodate the entire gasket body including the portion forming the cylinder opening in the mold to enable the molding of the elastomeric sealing ribs thereon.
This molding operation may include a central distribution of the molding material to the recesses in the mold parts in which the sealing strips are to be formed. The closure of the mold is effected by a press and it is difficult to accommodate in a single mold or in a single molding press, more than one or at most a few gasket bodies because of the size of the body which must be incorporated in the mold.
As a consequence, one must either make use of extremely large presses with comparatively high capital cost, or a number of presses with correspondingly high investments.
Another disadvantage of conventional gaskets of this type is that the proximity of the fire ring to the sealing rings is such that there is a significant conduction of heat to the latter so that the elastomeric materials which are used must have a refractory characteristic themselves, i.e. must be of a quality enabling them to resist elevated temperatures which may be as high as 250.degree. C. This of course requires the use of elastomers that are highly expensive and which require significant polymerization times so that the manufacturing cost is considerable and the rate of manufacture is limited.